U.S. patent number 10,138,425 [Application Number 15/310,683] was granted by the patent office on 2018-11-27 for delayed coke drum quench systems and methods having reduced atmospheric emissions.
This patent grant is currently assigned to Bechtel Hydrocarbon Technology Solutions, Inc.. The grantee listed for this patent is Bechtel Hydrocarbon Technology Solutions, Inc.. Invention is credited to Scott Alexander, Richard Heniford, John D. Ward.
United States Patent |
10,138,425 |
Ward , et al. |
November 27, 2018 |
Delayed coke drum quench systems and methods having reduced
atmospheric emissions
Abstract
Systems and methods for reducing atmospheric emission of
hydrocarbon vapors by flashing off hydrocarbon vapors in an
overflow drum where the pressure is ultimately reduced to 0 psig
and then flashing off any remaining hydrocarbon vapors in an
overflow tank wherein the pressure in the overflow tank is reduced
to 0 psig by an overflow ejector.
Inventors: |
Ward; John D. (Katy, TX),
Heniford; Richard (Katy, TX), Alexander; Scott
(Billings, MT) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bechtel Hydrocarbon Technology Solutions, Inc. |
Houston |
TX |
US |
|
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Assignee: |
Bechtel Hydrocarbon Technology
Solutions, Inc. (Houston, TX)
|
Family
ID: |
58387079 |
Appl.
No.: |
15/310,683 |
Filed: |
April 8, 2016 |
PCT
Filed: |
April 08, 2016 |
PCT No.: |
PCT/US2016/026699 |
371(c)(1),(2),(4) Date: |
November 11, 2016 |
PCT
Pub. No.: |
WO2017/052692 |
PCT
Pub. Date: |
March 30, 2017 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20180187086 A1 |
Jul 5, 2018 |
|
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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62221501 |
Sep 21, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10B
39/04 (20130101); C10B 55/00 (20130101); C10G
9/005 (20130101) |
Current International
Class: |
C10B
55/00 (20060101); C10G 9/00 (20060101); C10B
39/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Shane Thomas, International Search Report and Written Opinion of
the International Searching Authority, Application No.
PCT/US16/26699, dated Jul. 12, 2016, 7 pages, International
Searching Authority, US. cited by applicant .
Blaine R Copenheaver, Notice of Transmittal of the International
Search Report and The Written Opinion of the International
Searching Authority, International Application No.
PCT/US2014/028878, dated Jul. 29, 2014, 11 pages, International
Searching Authority, Alexandria, Virginia. cited by applicant .
Jill Warden, Notification of Transmittal of International
Preliminary Report on Patentability, International Application No.
PCT/US2014/026878, dated Jan. 22, 2015, 7 pages, International
Preliminary Examining Authority, Alexandria, Virginia. cited by
applicant .
Search Report for Patent Application, ROC (Taiwan) Patent
Application No. 105130514, dated Jul. 9, 2017, 1 page, Taiwan.
cited by applicant .
Kihwan Moon, International Preliminary Report on Patentability, PCT
Application No. PCT/US2016/026699, dated Apr. 5, 2018, 6 pages,
International Bureau of WIPO, Geneva Switerzland. cited by
applicant.
|
Primary Examiner: Miller; Jonathan
Assistant Examiner: Pilcher; Jonathan Luke
Attorney, Agent or Firm: Crain, Caton & James
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The priority of PCT Patent Application No. PCT/US2016/0026699,
filed on Apr. 8, 2016, which claims the benefit of U.S. Provisional
Application 62/221,501, filed on Sep. 21, 2015, is hereby claimed,
and the specification thereof is incorporated herein by reference.
Claims
The invention claimed is:
1. A system for reducing atmospheric emissions of hydrocarbon
vapors in a delayed coke drum quench overflow system, which
comprises: an overflow drum connected to a blowdown header line for
reducing hydrocarbon vapors and producing a vapor overflow
remainder and a liquid overflow remainder; an overflow tank,
connected to the overflow drum by a liquid overflow remainder line,
for separating at least one of skim oil, water, coke fines, and
tank vapor from the liquid overflow remainder; an overflow drum
vapor line in fluid communication with the overflow drum for
transmitting the vapor overflow remainder to a steam line; and a
tank vapor line in fluid communication with the overflow tank for
transmitting the tank vapor to an overflow ejector, wherein the
overflow ejector includes an inlet in fluid communication with the
tank vapor line and an outlet in fluid communication with the steam
line for reducing the pressure in the overflow tank to 0 psig.
2. The system of claim 1, further comprising a suction pressure
controller, the suction pressure controller in communication with
the inlet of the overflow ejector and the outlet of the overflow
ejector, for preventing a vacuum in the tank vapor line.
3. The system of claim 2, further comprising: a liquid overflow
remainder valve in the liquid overflow remainder line and a limit
controller associated with the overflow drum and adapted to control
the liquid overflow remainder valve for maintaining a constant
level in the overflow drum.
4. The system of claim 3, further comprising: a non-air gas supply
in communication with the overflow tank; and a non-air gas valve
intermediate the non-air gas supply and the overflow tank for
preventing a vacuum in the overflow tank.
5. The system of claim 4, further comprising: a check valve, the
check valve in the steam line intermediate an overhead line, the
overhead line intermediate a quench tower and a blowdown condenser,
and the overflow drum vapor line, to prevent flow from the quench
tower to the overflow tank or the overflow drum.
6. The system of claim 5, further comprising: a steam supply in
connection with the overflow tank; and an overflow ejector valve
intermediate the steam supply and the overflow ejector to open a
flow of steam to the overflow ejector.
7. The system of claim 1, further comprising: an overflow line in
communication with the overflow tank and a quench water tank for
communicating water from the overflow tank to the quench water
tank.
8. The system of claim 7, further comprising: an overflow line
valve in the overflow line for limiting a flow of water through the
overflow water line.
9. The system of claim 8, further comprising: a coke cutting line
connected to the quench water tank; a quench water line connected
to the quench water tank; a water in-flow line from the quench
water line to the overflow tank; and a water inflow valve in the
water in-flow line, intermediate the quench water line and the
overflow tank, for adjusting a volume of water in the overflow
tank.
10. The system of claim 1, further comprising: a coke cutting line
connected to the overflow tank; and a quench water line connected
to the overflow tank.
11. A method for reducing atmospheric emissions of hydrocarbon
vapors in a delayed coke drum quench overflow system, which
comprises: producing a vapor overflow remainder and a liquid
overflow remainder from an overflow drum; separating at least one
of skim oil, water, coke fines, and tank vapor from the liquid
overflow remainder in an overflow tank; transmitting the vapor
overflow remainder to a steam line; transmitting the tank vapor to
the steam line through an overflow ejector; and reducing the
pressure of the overflow tank to 0 psig.
12. The method of claim 11, further comprising: introducing water
into the overflow drum to maintain a constant level of water in the
overflow drum.
13. The method of claim 12, further comprising: introducing a
non-air gas into the overflow tank to prevent a vacuum in the
overflow tank.
14. The method of claim 13, further comprising: positioning a check
valve in the steam line to prevent flow from a quench tower to the
overflow tank or the overflow drum.
Description
FIELD OF THE DISCLOSURE
The present disclosure generally relates to delayed coking drum
quench systems and methods having reduced atmospheric emissions.
More particularly, the present disclosure relates to reducing
atmospheric emissions of hydrocarbon vapors by flashing off
hydrocarbon vapors in an overflow drum wherein the pressure is
reduced by an overhead ejector to 0 psig, and where any remaining
hydrocarbon vapors are flashed off through the overflow ejector to
the blowdown condenser.
BACKGROUND
Coking is one of the older refining processes. The purpose of a
delayed coking plant is to convert heavy residual oils (e.g. tar,
asphalt, etc.) into lighter, more valuable motor fuel blending
stocks. Refinery coking is controlled, severe, thermal cracking. It
is a process in which the high molecular weight hydrocarbon residue
(normally from the bottoms of the vacuum flasher in a refinery
crude unit) are cracked or broken up into smaller and more valuable
hydrocarbons.
Coking is accomplished by subjecting the feed charge to an extreme
temperature of approximately 930.degree. F. that initiates the
cracking process. The light hydrocarbons formed as a result of the
cracking process flash off and are separated in conventional
fractionating equipment. The material that is left behind after
cracking is coke, which is mostly carbon. In addition to coke,
which is of value in the metal industry in the manufacture of
electrodes, fuel coke, titanium dioxide, etc., the products of a
delayed coking plant include gas (refinery fuel gas), liquefied
petroleum gas, naphtha, light gas oil, and heavy gas oil.
Most of the world's coking capacity is generated by delayed coking
processes. Delayed coking can be thought of as a continuous batch
reaction. The process makes use of paired coke drums. One drum (the
active drum) is used as a reaction vessel for the thermal cracking
of residual oils. This active drum slowly fills with coke as the
cracking process proceeds. While the active drum is being filled
with coke, a second drum (the inactive drum) is in the process of
having coke removed from it. The coke drums are sized so that by
the time the active drum is filled with coke, the inactive drum is
empty. The process flow is then switched to the empty drum, which
becomes the active drum. The full drum becomes the inactive drum
and is emptied or decoked. By switching the process flow back and
forth between the two drums in this way, the coking operation can
continue uninterrupted.
In operation, after being heated in a direct-fired furnace, the oil
is charged to the bottom of the active coke drum. The cracked light
hydrocarbons rise to the top of the drum where they are removed and
charged to a fractionator for separation. The heavier hydrocarbons
are left behind, and the retained heat causes them to crack to
coke.
In FIG. 1, a schematic diagram illustrates one example of a delayed
coking closed blowdown system (hereinafter "delayed coking quench
system"), where the effluent from the inactive drum is processed.
The quenching of the inactive coke drum produces large quantities
of steam with some hydrocarbons which are processed in this
system.
A quench tower 106, a blowdown condenser 122 and a settling drum
124 form a closed blowdown system, which is used to recover
effluent from the coke drum steaming, quenching and warming
operations.
In conventional systems, a blowdown header line 104 communicates
the hot vapor from a coke drum overhead line 101 to a quench tower
106 during the steaming and water quenching operation.
Just upstream of the quench tower 106, the hot vapor is quenched by
a controlled injection of water from the process. During the water
quenching operation, the overhead stream from the quench tower 106,
is substantially steam with small amounts of hydrocarbons, and is
sent in an overhead line 120 to the blowdown condenser 122.
The blowdown condenser 122 condenses the bulk of the overhead
stream to form a blowdown condenser outlet stream which is
communicated in the blowdown condenser outlet stream line 123 to a
blowdown settling drum 124.
In the settling drum 124, the blowdown condenser outlet stream is
separated into a sour water stream 126, a light slop oil stream 132
and a hydrocarbon vapor stream 127. The hydrocarbon vapor stream
127 is sent to the blowdown ejector 158 and then to the
fractionator overhead system 160. The light slop oil stream 132 is
returned to the quench tower 106. The blowdown ejector 158 is used
to reduce the pressure in the closed blowdown system and coke drum
at the end of the water quench prior to isolating a coke drum and
venting the coke drum to atmosphere. Alternatively, a compressor
may be used in place of a blowdown ejector 158. The blowdown
ejector, which may be steam-driven, is used to target 2 psig before
venting the drum to atmosphere. Effluent from blowdown ejector 158
is sent to the fractionator overhead system 160, and recovered to
the main process.
A quench water tank 140 is used to provide water to quench water
line 148 and to the coke cutting line 142.
During the quench operation the inactive coke drum is connected to
the closed blowdown system and the pressure in the inactive coke
drum is essentially the same as the pressure in the closed blowdown
system. At the end of the quench operation, the inactive coke drum
is isolated from the closed blowdown system and is vented to the
atmosphere. An ejector or small compressor may be used in a line
containing the hydrocarbon vapor stream 127 to reduce the pressure
in the closed blowdown system and inactive coke drum to about 2
psig or less prior to isolating and venting the inactive coke drum
as required by current environmental regulation guidelines. Despite
venting the inactive coke drum to the atmosphere at 2 psig, a plume
of steam is produced that may contain hydrocarbon vapors (e.g.
methane, ethane, hydrogen sulfide) and coke fines (hereinafter
collectively "atmospheric emissions"). Maintaining a pressure of 2
psig in the inactive coke drum prior to venting to the atmosphere
is also an issue because the coke drum pressure can spike due to
continuing heat evolution from the coke bed after isolation from
the closed blowdown system. On some older units, which start to
vent at around 15 psig, noise is also a significant issue.
It is known that a delayed coking quench system may be modified to
include a coke drum quench overflow system to provide the benefit
of overflowing a coke drum at the end of the quench operation.
Existing overflow systems are varied and some have been known to
generate undesirable odors, and gas releases or fires, plugging
exchangers and residual coke fines in lines that are flushed into
other equipment when the coke drums are returned to the fill cycle
because the overflow stream can contain significant atmospheric
emissions. In addition, many existing overflow systems do not
minimize atmospheric emissions, and merely relocate the source of
the atmospheric emissions.
Because some existing overflow systems have American Petroleum
Institute ("API") separators or other equipment open to the
atmosphere, there can be atmospheric emissions, which is a serious
problem. When the overflow stream is sent through an air cooler
without being properly filtered, the air cooler can plug, which is
also a problem in some existing overflow systems. In parts of the
piping system used by existing overflow systems, coke fines are
often left after the overflow operation, which are then flushed
into the quench tower or fractionator when returning to the normal
valving arrangement. A delayed coking unit that produces shot coke
can result in larger amounts of oil and coke fines in the quench
overflow stream, which is more problematic to handle.
SUMMARY
The present disclosure therefore, meets the above needs and
overcomes one or more deficiencies in the prior art by providing
systems and methods for reducing atmospheric emissions of
hydrocarbon vapors by flashing off hydrocarbon vapors in an
overflow drum where the pressure is ultimately reduced to 0 psig
and then flashing off any remaining hydrocarbon vapors in an
overflow tank wherein the pressure in the overflow tank is reduced
to 0 psig by an overflow ejector.
In one embodiment, the present disclosure includes a system for
reducing atmospheric emissions of hydrocarbon vapors in a delayed
coke drum quench overflow system, which comprises: i) an overflow
drum connected to a blowdown header line for reducing hydrocarbon
vapors and producing a vapor overflow remainder and a liquid
overflow remainder; ii) an overflow tank connected to the overflow
drum by a liquid overflow remainder line for separating at least
one of skim oil, water, coke fines, and tank vapor from the liquid
overflow remainder; iii) an overflow drum vapor line in fluid
communication with the overflow drum for transmitting the vapor
overflow remainder to a steam line; and iv) a tank vapor line in
fluid communication with the overflow tank for transmitting the
tank vapor to an overflow ejector, wherein the overflow ejector
includes an inlet in fluid communication with the tank vapor line
and an outlet in fluid communication with the steam line for
reducing the pressure in the overflow tank to 0 psig.
In another embodiment, the present disclosure includes a method for
reducing atmospheric emissions of hydrocarbon vapors in a delayed
coke drum quench overflow system, which comprises: i) producing a
vapor overflow remainder and a liquid overflow remainder from an
overflow drum; ii) separating at least one of skim oil, water, coke
fines, and tank vapor from the liquid overflow remainder in an
overflow tank; iii) transmitting the vapor overflow remainder to a
steam line; iv) transmitting the tank vapor to an inlet of an
overflow ejector; and v) reducing the pressure of the overflow tank
to 0 psig.
Additional aspects, advantages and embodiments of the disclosure
will become apparent to those skilled in the art from the following
description of the various embodiments and related drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is described below with references to the
accompanying drawings, in which like elements are referenced with
like numerals, wherein:
FIG. 1 is a schematic diagram illustrating one example of a
conventional delayed coking quench system.
FIG. 2 is a schematic diagram illustrating a conventional delayed
coking quench system and one embodiment of a delayed coking quench
overflow system according to the present disclosure.
FIG. 3 is a schematic diagram illustrating a conventional delayed
coking quench system and another embodiment of a delayed coking
quench overflow system according to the present disclosure.
DETAILED DESCRIPTION
The subject matter of the present disclosures is described with
specificity, however, the description itself is not intended to
limit the scope of the disclosure. The subject matter thus, might
also be embodied in other ways, to include different structures,
steps and/or combinations similar to and/or fewer than those
described herein, in conjunction with other present or future
technologies. Moreover, although the term "step" may be used herein
to describe different elements of methods employed, the term should
not be interpreted as implying any particular order among or
between various steps herein disclosed unless otherwise expressly
limited by the description to a particular order. While the
following description refers to delayed coking drum quench
operations, the systems and methods of the present disclosure are
not limited thereto and may be applied in other operations to
achieve similar results.
Referring now to FIG. 2, a schematic diagram illustrates a
conventional delayed coking quench system and one embodiment of a
delayed coking quench overflow system according to the present
disclosure.
In operation, at the end of the water quench operation, water
covers the coke bed in the coke drum and is allowed to overflow
into an overflow drum 208 and overflow tank 216. This is
accomplished when a level switch on the coke drum causes a valve
204 in the blowdown header line 104 to close and opens a supply
line valve 206 in the supply line 207 to the overflow drum 208. To
ensure the coke drum relief valve discharge remains operable, valve
204 is positioned upstream of the coke drum relief valve discharge
102 to the quench tower 106.
In the overflow drum 208, hydrocarbon vapors are preferably flashed
off, reducing or eliminating atmospheric emissions. The overflow
drum 208 is in communication with a steam/hydrocarbon vapor line
262 via an overflow drum vapor line 209, to communicate the
flashed-off hydrocarbons and steam, the vapor overflow remainder,
to the overhead hydrocarbon steam stream line 120 for delivery to
the blowdown condenser 122 and, ultimately, the blowdown ejector
158. The overflow drum vapor line 209 is thus in fluid
communication with the overflow drum 208 for transmitting the vapor
overflow remainder to a steam line 262. The communication with the
steam/hydrocarbon vapor line 262, which operates at 0-2 psig,
ensures the overflow drum 208 likewise operates at approximately
0-2 psig, and therefore maximizes the volume of vapor overflow
remainder flashed off through the blowdown condenser 122. The
overflow drum 208 is thus connected to a blowdown header line 104
for reducing hydrocarbon vapors and producing a vapor overflow
remainder and a liquid overflow remainder.
A liquid overflow remainder line 210 in communication with the
bottom of the overflow drum delivers the bulk of the overflow
stream, the liquid overflow remainder, containing water, liquid
hydrocarbons, and coke fines, to an overflow tank 216. A liquid
overflow remainder valve 212 in the liquid overflow remainder line
210 controls the flow through the liquid overflow remainder line
210 by the action of a level controller 214, which maintains a
constant level in the overflow drum 208.
The overflow tank 216 has sufficient residence time to allow
separation of oil, water and coke fines. The oil is skimmed off and
sent to the settling drum 124. The water is sent to the quench
water tank 140. The coke fines are drained to the coke pit. In the
overflow tank 216, the overflow drum bottom stream is collected and
temporarily retained, permitting separation of the overflow water
and the liquid hydrocarbons. The coke fines separate within the
water phase. A coke fines line 228 permits water laden with
concentrated coke fines to exit the overflow tank 216 and permits
delivery to the coke pit. A coke fines valve 230 is provided in the
coke fines line 228 to permit draining of the water laden with
concentrated coke fines. In operation, coke fines valve 230 is
opened periodically, such as once-per-shift.
In the overflow tank 216, the overflow water is removed from the
overflow tank 216 by an overflow water line 232 and provided to the
quench water tank 140. Preferably, the overflow water line 232 is
positioned appropriately on the side of the overflow tank 216 to
draw only overflow water, rather than the liquid hydrocarbons or
the coke fines. An overflow water pump 234 may be positioned in the
overflow water line 232 to aid in removal of the overflow water
from the overflow tank 216 and transmission to the quench water
tank 140. An overflow water valve 238 may also be positioned within
the overflow water line 232 to terminate flow through the overflow
water line 232 when desired. The overflow water valve 238 may be
controlled by a flow controller with a level override associated
with the overflow tank to avoid a low level in the tank and
cavitation of the pump. Overflow water, free of hydrocarbons, is
therefore transmitted from the overflow tank 216 to the quench
water tank 140 for use in the quench process and to make volume
available in the overflow tank 216 for the next overflow operation.
The overflow tank 216 is therefore connected to the overflow drum
208 by a liquid overflow remainder line 210 for separating at least
one of skim oil, water, coke fines, and tank vapor from the liquid
overflow remainder.
As needed, a water-inflow line 218, drawing quench water from the
quench water tank 140, may be provided to introduce quench water to
the overflow tank 216 to adjust volume in the overflow tank 216 as
needed. A water-inflow valve 220 may be provided in the
water-inflow line 218 to control the flow through the water-inflow
line 218. The water-inflow valve 220 may be controlled manually, or
by a flow controller, as well as other control systems known in the
art.
In the overflow tank 216, the liquid hydrocarbons, found as skim
oil, are removed from the overflow tank 216 by a skim oil line 244
and provided to the settling drum 124. A drawoff tray is located
high in the overflow tank 216. As the skim oil is separated from
the overflow water, the skim oil collects in the drawoff tray. When
the level in the drawoff tray is sufficient, the skim oil is
transmitted via the skim oil line 244 and the outlet stream line
123 to the settling drum 124. The determination of sufficiency may
be accomplished by a level controller, or by other control systems
known in the art. A skim oil pump 240 may be positioned in the skim
oil line 244 to aid in removal of the skim oil from the overflow
tank 216 and transmission to the settling drum 124. A skim oil flow
control valve 248 may also be positioned within the skim oil line
244 to terminate flow through the skim oil line 244 if the level in
the overflow tank draw tray is low.
To ensure a vacuum does not arise in the overflow tank 216, a
non-air gas, preferably a fuel gas, natural gas, or nitrogen gas,
is introduced to the overflow tank 216 by a non-air gas line 256.
The non-air gas avoids the potential for air ingress into the
system, which prevents the potential for hazardous air-hydrocarbon
mixtures, and serves as a vacuum-breaker gas. A non-air gas valve
254, preferably controlled by a pressure controller and set to open
on very low pressure, may be provided in the non-air gas line 256
to preclude a vacuum from arising. A non-air gas supply may be
provided in communication with the overflow tank 216 together with
a non-air gas valve intermediate the non-air gas supply and the
overflow tank 216.
Any steam/hydrocarbon vapor, and non-air gas, the tank vapor, exits
the overflow tank 216 by a tank vapor line 253 and is communicated
to the steam/hydrocarbon vapor line 262 through an overflow ejector
280.
The communication with the overflow ejector 280, ensures overflow
tank 216 operates at 0 psig, and therefore reduces the vapor
pressure of the liquids in the overflow tank 216, so that when
exposed to atmosphere, essentially no vapor is generated.
The overflow ejector 280 is in communication with the
steam/hydrocarbon vapor line 262 and the tank vapor line 253,
having an inlet in communication with the tank vapor line 253 and
an outlet in communication with the steam/hydrocarbon vapor line
262. The overflow ejector 280 reduces the pressure in the overflow
tank 216 to 0 psig. The outflow from overflow ejector 280, together
with the remaining vapor in the overflow drum vapor line 209 are
provided to the blowdown condenser 122 with the content of the
overhead hydrocarbon steam stream line 120 to condense the steam
and hydrocarbon vapor. Steam, the motive fluid for the overflow
ejector 280 is provided from an overflow ejector steam line 266. An
overflow ejector steam line valve 270 may be provided in the
overflow ejector steam line 266 to open and allow the flow of steam
to the overflow ejector 280. The overflow ejector steam line valve
270 is an on/off valve which can be opened and closed from the
control room, but may be controlled by other control systems known
in the art. The overflow ejector 280 may include a suction pressure
controller 291 in communication with the overflow ejector discharge
to control pressure in the overflow tank. The setting on this
controller can be 0 psig. The suction pressure controller 291 is in
communication with the inlet of the overflow ejector 280 and the
outlet of the overflow ejector 280, for preventing a vacuum in the
tank vapor line 253 and therefore in the overflow tank 216.
An overflow ejector steam line check valve 290 may be positioned in
the overflow ejector steam line 266 intermediate the communication
from the overflow ejector 280 and the junction with the overhead
hydrocarbon steam stream line 120 to prevent backflow from the
quench tower 106 to the overflow tank 216 and overflow drum
208.
Referring now to FIG. 3, a schematic diagram illustrates a
conventional delayed coking quench system and another embodiment of
a delayed coking quench overflow system according to the present
disclosure.
In another embodiment, the function of the quench water tank 140 is
accomplished in a quench water/overflow tank 316, a modification of
the overflow tank 216. The quench water/overflow tank 316 includes
all elements associated with the overflow tank 216 together than
the coke cutting line 342 and a quench water line 348 associated
with the quench water tank 140. The overflow water pump 234 and the
overflow water line 232, and the water-inflow line 218 and the
water-inflow valve 220 shown in FIG. 2 are eliminated.
The delayed coking quench overflow systems illustrated in FIGS. 2-3
effectively minimize atmospheric emissions, which can be applied to
delayed coking units that produce shot coke as well as sponge coke.
The delayed coking quench overflow systems reduce atmospheric
emission of hydrocarbon vapors by flashing off steam and
hydrocarbon vapors in an overflow drum--wherein the pressure is
reduced by a blowdown ejector to essentially 0-2 psig--and
similarly where any remaining hydrocarbon vapors are flashed off
from an overflow tank--wherein pressure is reduced to essentially 0
psig from the overflow ejector--to the blowdown condenser.
The present disclosure thus provides a method for reducing the
atmospheric emissions of hydrocarbon vapors in a delayed coke drum
quench overflow system by producing a vapor overflow remainder and
a liquid overflow remainder from the overflow drum 208, separating
at least one of skim oil, water, coke fines, and tank vapor from
the liquid overflow remainder in the overflow tank 216,
transmitting the vapor overflow remainder to the steam line 262,
transmitting the tank vapor to an inlet of the overflow ejector
280, and reducing the pressure of the overflow tank 216 to 0 psig.
The method may further include introducing water into the overflow
drum 208 to maintain a constant level of water in the overflow drum
208 or introducing a non-air gas into the overflow tank 216 to
prevent a vacuum in the overflow tank 216. The method may also
include positioning a check valve 290 in the steam line 262 to
prevent flow from a quench tower 106 to the overflow tank 216 or
the overflow drum 208.
Thus, according to the present disclosure, emissions are minimized
by recovering all hydrocarbon/steam vapor and oil to the existing
blowdown system--a closed system. The overflow ejector 280 reduces
the pressure in the overflow tank 216, and the associated tank
vapor line 253 to 0 psig. The associated water streams--the coke
fines line 228, and the overflow water line 232--are therefore also
at 0 psig, eliminating potential vapor when these streams are
exposed to atmosphere. Operation of the overflow tank 216, is at
the same pressure as the quench water tank 140, which may allow the
use of one tank to perform the functions of both an overflow tank
and a quench water tank. In addition, the delayed coking quench
overflow systems illustrated in FIGS. 2-3 may be retrofitted to
conventional delayed coking quench systems.
While the present disclosure has been described in connection with
presently preferred embodiments, it will be understood by those
skilled in the art that it is not intended to limit the disclosure
to those embodiments. For example, it is anticipated that by
routing certain streams differently or by adjusting operating
parameters, different optimizations and efficiencies may be
obtained, which would nevertheless not cause the system to fall
outside of the scope of the present disclosure. It is therefore,
contemplated that various alternative embodiments and modifications
may be made to the disclosed embodiments without departing from the
spirit and scope of the disclosure defined by the appended claims
and equivalents thereof.
* * * * *